The present invention relates to a method and to an arrangement for compiling the transmitter-receiver relationship in a radio system.
A radio connection can be established between a transmitter and a receiver in a radio communications system. The connection is two-directional, and one refers to a downlink that forms the connection in a direction away from a base station in the radio communications system to a mobile station, and an uplink which forms the connection in the opposite direction, i.e. from the mobile station to the base station. Transmission and reception of radio traffic for different connections takes place on radio channels that can be defined by a given frequency in an FDMA system (Frequency Division Multiple Access) or by a combination of a given frequency and a given time slot in a system that uses TDMA (Time Division Multiple Access).
The radio channels available in an FDMA system and a TDMA system can be reused. Thus, the signal strength received in a receiver on a radio channel may include a signal strength contribution from all transmitters that transmit on this radio channel. The distance between two transmitters that transmit on one and the same radio channel, the so-called repetitive distance will preferably be sufficiently great to ensure that the desired received signal is not subjected unduly to co-channel interference.
By interference is meant the sum of the signal strengths of all undesirable signals received on the radio channel used. These undesirable signals derive primarily from other connections that use the same radio channel in neighbouring cells of the radio communications system.
A poor connection of unacceptable quality in a radio communications system may be due, among other things, to the fact that the ratio between the signal strength of the desired signal and the interference is too low. The signal strength ratio between the desired signal (carrier) and the disturbing signals (interference) is normally given as the C/I ratio (Carrier to Interference ratio) and is a measurement of channel quality.
The U.S. Pat. No. 5,157,709xe2x80x94Ohteru, teaches an adaptive radio communications system that includes a control station which sets up an interference matrix for the interference values between base stations. Each base station measures power levels on signals that are received on unoccupied radio channels. Information relating to received power levels on unoccupied radio channels is forwarded to the control station together with the radio channel and base station identity. The control station generates on the basis of this information an interference matrix which is used in adaptive allocation of channels to the base stations. U.S. Pat. No. 5,603,092xe2x80x94Stjernholm, also teaches a method of estimating interference. The interference is used for statistical evaluation. Measuring of traffic in other cells is carried out in both cases, i.e. in both Ohteru and Stjernholm. When frequencies are repeated by different transmitters located at different distances from a receiver, the strength of the signal received from these transmitters will vary. When several transmitters send simultaneously on one and the same channel, it is normally only possible to identify the strongest signal. The result is that only a few observations are obtained from remote cells. The method to Ohteru involves creating an interference matrix that contains information relating to mutually interfering cells and how often such interference occurs. The method does not, on the other hand, involve transmitter-receiver amplification between the cells. The method taught by Stjernholm involves measuring the magnitude of the interference. The magnitude of the interference magnitude, however, will depend on transmission power. One drawback in this regard is that dynamic power regulation results in difficulties in power level distribution, when said level changes. Furthermore, difficulties arise in measuring the relationship of a receiver to a remote transmitter when the power output of these transmitters is maintained at a low level in order to avoid interference situations.
When creating a frequency plan in a radio system for instance, it is desirable to know what affect an individual transmitter in a relatively wide area in the system will have on receivers in the system. It is also desirable to compile in a simple fashion information where relationships between each individual transmitter, irrespective of its transmitted power, and each receiver can be predicted.
The present invention addresses the problem of compiling information that is indicative of how an individual transmitter in a radio system will influence a receiver in the system, i.e. establish a relationship between a transmitter and receiver, in a simple manner. Another problem addressed by the invention is to establish how one or more different transmitters in a radio system each influence one or more receivers in the system, and to compile this information in a form suited for later use.
The problems addressed by the invention are solved by measuring the amplification of a signal transmitted with known power by a transmitter. Upon reception in one or more receivers, the signal is guaranteed to be a solitary signal, i.e. a lone signal, received at a given point in time or at a given geographical position. The method is repeated for several transmitters and the values measured are combined in a central unit in the system.
More specifically, the problems are solved by sending from a transmitter a radio signal of known power. The signal is guaranteed to be a solitary signal by choosing a certain type of signal for reception, this signal type being sent solely during a relatively short period on a channel which is essentially silent. The power of the signal is measured upon reception in one or more receivers and the amplification is calculated for each received signal as the quotient between received power and transmitted power. The calculated amplification value is stored in a storage location together with information disclosing the whereabouts of the transmitter in the radio system when transmitting the signal. The method is repeated with other transmitters in the system. A matrix comprising relationships between transmitter and receiver is stored in a central unit in the system.
An object of the present invention is to create in a simple manner a dynamic matrix that shows the relationships between transmitters that are located in different radio trafficked areas in a radio system and receivers in said system. The matrix is used as a measurement of the probability of a transmitter in the radio trafficked area relating to the receiver in a certain way on a later occasion. The matrix is used to improve system performance.
One advantage of the invention resides in the simplicity of creating the dynamic transmitter/receiver relationship matrix. The relationship matrix can then be used in connection with frequency planning for instance, subsequent to studying the stored measured values in the relationship matrix and subsequent to determining the probable effect in the system of choosing different frequencies. Alternatively, lists of neighbouring cells, or adjacent cells, can be created in a mobile system subsequent to reading from the matrix the relationship of transmitters to base stations when these transmitters were located in different cell areas of the system. Furthermore, adaptive channel allocation can be made in a radio system subsequent to studying the stored values in the matrix and thereafter determining the interference effect in the system with different channel selections when establishing a connection between a transmitter and a receiver.
Another advantage afforded by the invention is that the relational matrix can be established even when low transmitter powers are normally desired, since the transmission of the solitary signal will not interfere with other transmissions. This enables the transmitters to have a higher output power, which, in turn, enables the relational matrix to be created for wide geographical areas.
The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.